This recent study found that female rats fed Roundup-tolerant corn developed large mammary tumors, and many had pituitary problems. The male rats fed the genetically engineered corn suffered from liver problems. And both males and females suffered from significant kidney problems.

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The study began by growing Monsanto’s NK603 Roundup-tolerant corn and the most similar non-GMO strain in the same location, under similar conditions, spaced “at a sufficient distance to avoid cross-contamination.” One field of NK603 was treated with Roundup. Another field of NK603 was not treated with Roundup. Following harvest, the researchers had three groups of corn: non-GMO untreated corn, GMO untreated corn, and GMO treated corn.

The study used 200 rats, 100 male and 100 female. The rats used were Virgin albino Sprague-Dawley rats, which are the same strain used in many previous feeding trials. A control group of 10 rats of each sex had access to plain water and standard non-GMO feed. Six groups received feed formulated with 11, 22 and 33% GMO corn, either treated or not with Roundup. The remaining three groups ate the control diet but drank water supplemented with Roundup at different levels. The animals’ health was monitored twice weekly, blood and urine tests were performed 11 times at intervals of one to three months, and the study lasted two years. During the study, any rats who were severely suffering were put down and their organs were collected for analysis.

“Control male animals survived on average 624 ± 21 days, whilst females lived for 701 ± 20, during the experiment, plus in each case 5 weeks of age at the beginning and 3 weeks of stabilization period. After mean survival time had elapsed, any deaths that occurred were considered to be largely due to aging.” Of the 20 control rats (10 male, 10 female), “30% control males (three in total) and 20% females (only two) died spontaneously prior to the time at which their deaths would be attributed to old age.”

“Up to 14 months, no animals in the control groups showed any signs of tumors whilst 10–30% of treated females per group developed tumors, with the exception of one group (33% GMO + R). By the beginning of the 24th month, 50–80% of female animals had developed tumors in all treated groups, with up to 3 tumors per animal, whereas only 30% of controls were affected. The R [Roundup] treatment groups showed the greatest rates of tumor incidence with 80% of animals affected with up to 3 tumors for one female, in each group.”

The most affected organ in females was the mammary, followed by the pituitary gland. In males, the most affected organ was the liver, together with the hepatodigestive tract and kidneys. The study includes several grotesque photos of rats with large tumors.

Although the treatment groups showed increased mortality and morbidity compared to the controls, the results were not in proportion to the amount of GM maize and Roundup each group consumed. The study authors noted that this is “often the case for hormonal diseases.”

The authors link the large number of mammary tumors to estrogen, writing that “even at the very lowest dose administered, R has been shown to disrupt aromatase which synthesizes estrogens (Richard et al., 2005), but to also interfere with estrogen and androgen receptors in cells (Gasnier et al., 2009). In addition, R appears to be a sex endocrine disruptor in vivo, also in males (Romano et al., 2010). Sex steroids are also modified in treated rats. These hormone-dependent phenomena are confirmed by enhanced pituitary dysfunction in treated females.”

For rats fed Roundup Ready corn (NK603) that was grown without any use of Roundup, “similar effects with respect to enhanced tumor incidence and mortality rates were observed.” The authors conclude that both Roundup itself and the Roundup-tolerant corn “may cause hormonal disturbances in the same biochemical and physiological pathway.”